Teiichi Homma

Investigation of Vapor Adsorption on Molybdenum Disulfide Surfaces by Auger Electron Spectroscopy

The adsorption characteristics of the cleavage and edge surfaces of MoS2 were studied by Auger electron spectroscopy, and the following conclusions were obtained. The cleavage surface of MoS2 has difficulty in adsorbing the vapors, and the adsorbed vapor is easily evaporated from the surface in vacuum. On the contrary, the edge surface of MoS2 adsorbs vapors easily, and is difficult to evaporate. These experimental results could explain the difference in the frictional behaviors of cleavage and edge surfaces of MoS2. Sulfur is usually richer than the estimated stoichiometric value on the MoS2 surface, and even on the adsorbed surface. Ion etching can reduce the sulfur contents to the stoichiometric value. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in New Orleans, Louisiana, October 5–7, 1981

Nucleation and Growth Behavior of Oxide on Copper Single Crystals: Their Roles in Kinetics

A short circuit diffusion model due to a mosaic structure of the oxide has been proposed on the features of the oxidation rate anisotropy of single crystals of copper and nickel in the growth stage of continuous oxide films. In order to make clear the influence of the mosaic structure on the oxidation rate anisotropy, a correlation between the mosaic structure and the kinetic behavior was studied on the (001) face of copper by means of RHEED and microbalance techniques with UHV systems. The mosaic structure which depends on the epitaxial nucleation behavior in the early stage of oxidation was controlled by changing an off angle of a specimen surface from the (001) face of copper. The results show that the nucleation and growth behaviors of oxide have a straight effect on the mosaic structure and in turn the oxidation kinetics due to the short circuit diffusion.

Electron diffraction study of the epitaxy of Cu2O on the (001) face of copper

The epitaxy of Cu2O crystal formed on the (001) face of copper during oxidation has been investigated with reflection HEED and electron microscope techniques. Carefully prepared Cu single crystals were used as substrates. A transitional epitaxial orientation of the oxide was found before completely developed twin oriented (111) epitaxy. For oxides formed in the early stage of oxidation, the (221) and the (332) epitaxies have been found. The misorientation of the surface affected these epitaxial aspects. The observed aspects may be explained being based on surface morphological structures as facets composed of (001), (111), and (113).

A New Model of Stress Generation During Scale Growth Limited by Cation/Vacancy Diffusion

The stress generation during growth of cation-diffusing scales on pure metals is described in terms of intrinsic misfit for a grain boundary in oxides. This model is derived from the experimental observations by means of in situ x-ray strain measurements for the oxides grown on single crystal surfaces of copper. A change in the grain boundary structure which occurs by altering the relative amount of the twin-related oxide orientations present in the oxides on (001) or (111) face of copper leads to a change in the stress generation behavior. Compressive stresses are observed in the oxide with scale thickness of a few micrometers below the brittle-ductile transition temperature of the bulk oxide(300 ~ 400°C). The model which is based on the coincident site lattice model may explain the origin of stresses arising during the growth of cation-diffusing scales at rather moderate temperatures.